The present inventon relates to an improved process for producing an antimony-containing oxide catalyst supported on silica for use in a fluidized bed reaction. More particularly, the invention relates to a process for producing a catalyst for use in the oxidation, ammoxidation or oxidative dehydrogenation of organic compounds.
Many catalysts are known for use in the oxidation, ammoxidation, or oxidative dehydrogenation of organic compounds. Particularly good results are obtained by antimony-containing catalysts such as the antimony-tin oxide composition described in U.S. Pat. No. 3,152,170, the oxide composition containing antimony and iron, cobalt and/or nickel oxides described in Japanese Patent Publication No. 19111/63, and the antimony-uranium oxide composition described in U.S. Pat. No. 3,303,151.
In most cases, these catalysts are used as is supported on carriers such as silica, alumina, and titania for the primary purpose of imparting strength to the catalyst. Prior art techniques for attaining this purpose are described in U.S. Pat. Nos. 3,341,471, 3,657,155, and 3,686,138. While the techniques described in these prior art references relate to the production of antimony-containing oxide catalysts, they are not completely satisfactory for the purpose of producing catalysts having high activity and good physical properties. One problem common to the catalysts produced by these methods is low strength, which is particularly significant with respect to catalysts for use in fluidized bed reactions.
Sufficient catalyst strength is important for reactions in fluidized beds. Catalysts having high activity are not suitable for industrial use in their strength is low; in such a case, the catalyst loss is undesirably large (due to scattering to the outside of the system) and it becomes difficult to operate the system in a steady manner. Even if this worst case does not occur, the consumption of the catalyst is increased so as to undesirably increase the manufacturing cost of the end product.
Japanese Patent Application (OPI) No. 11045/83 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".) (corresponding U.S. Pat. No. 4,377,500) proposes using a mixture of fumed silica and silica sol as a carrier for supporting antimonate-based catalyst. It claims that by using this carrier material, an antimonate-based catalyst having good catalytic characteristics and high attrition resistance can be prepared. However, fumed silica is a powder which is to bulky that great inconvenience is involved in its handling. If fumed silica is mixed with silica sol, the resulting catalyst has low bulk density and low particle density as well as poor mechanical strength. Thus, it is seen that the method of Japanese Patent Application (OPI) No. 11045/83 (corresponding to U.S. Pat. No. 4,377,500) involves a complicated procedure in catalyst preparation, and the resulting catalyst has a relatively small strength that will cause increased catalyst loss during service.
A proposal for using a mixture of silica sols having different particle sizes with a view to producing a silica gel of low bulk density is shown in U.S. Pat. No. 3,397,153. The specification of this patent contains an Example which relates to the production of a catalyst supported on silica which is to be used in a fixed bed reaction and which contains phosphorus, molybdenum, and bismuth.
A catalyst for use in a fluidized bed reaction suffers from an increased catalyst loss if it has an excessively low bulk density and this is because the low bulk density leads to a catalyst of small strength which easily scatters to the outside of the reaction system. If, on the other hand, the catalyst has an excessively high bulk density, poor fluidization occurs in the bed. It is therefore desired that catalysts for use in fluidized bed reactions have a proper bulk density relative to the specific object and at the same time have sufficient mechanical strength.
U.S. Pat. No. 3,397,153 makes no mention of catalyst strength. Nor does it suggest the production of an antimony-containing oxide catalyst of the type contemplated by the present invention, i.e., a catalyst with improved strength for use in fluidized bed reactions.
Thus, the proposals made in U.S. Pat. Nos. 4,377,500 and 3,397,153 are not improvements of the methods described in U.S. Pat. Nos. 3,657,155 and 3,686,138, nor do they suggest the method of the present invention.